The hosts took the lead when man-of-the-match Isa Nacewa touched down with the opening score of the match after some smart interplay with Shane Horgan in the fourth minute.

But three Ryan Lamb penalties - after 10, 20 and 26 minutes - pushed the visitors into a 9-5 advantage.

There were some impressive cameos for Leinster in the first half with back rowers Stephen Keogh and Sean O'Brien showing real aggression alongside the industrious Shane Jennings.

Though Leinster threatened sporadically, it was the Exiles who showed greater potency in attack and they chalked up Steffon Armitage try and a penalty try, which Lamb converted at the Wesley end, to thank for their 21-5 half-time lead.

Leinster made a raft of substitutions in the second half as a number of players from Ireland's successful Churchill Cup campaign made their first starts of the season.

A Jonathan Sexton penalty on 58 minutes was just reward for a spell of Leinster pressure.

Fergus McFadden made a string of daring breaks, while replacement Kevin McLaughlin also impressed in the second half. 

Nonetheless, a late Lamb penalty restored London Irish's 16-point advantage and though the result was disappointing, it was a good physical workout for Michael Cheika's squad ahead of the start of the Magners League campaign next weekend.